The present invention pertains to a process for the thermal, thermomechanical, hydrothermal or hydrothermomechanical treatment of various natural or transformed alimentary, cosmetic, chemical or pharmaceutical products, in solid, piece, powder, paste, liquid, miscible or nonmiscible liquid mixture, etc. form by application of a cycle of pressure, temperature and/or humidity variation in a treatment chamber.
The treatment has multiple effects; the principal effect attained by the process according to the invention depends on the nature of the initial product introduced into the treatment chamber, the operating conditions employed and the envisaged final product.
This invention enables the precise control of multiple classic thermal processes by accelerating the kinetics, improving the quality of the finished products and reducing the energy consumption and reject rate. These processes generally pertain to the operations of pasteurization, sterilization and/or packaging of solid products in piece or powder form, the thermal modification of the materials (gelatinization, for example), their structure and/or their texture, or the separation of their compounds. These effects also include phase separation, especially the extraction of essential oils, fragrances or various components, as well as the improvement of the separation of other compounds (fats, oils, etc.). This treatment improves the quality of the product, especially by the concentration of certain compounds in relation to other constituents. The treatment can facilitate the peeling of fruits and vegetables, improve their pressing, increase the value of their by-products or reduce the number of technical steps in operations, etc. The present invention concerns the precise control of these operations by controlling the temperature and duration of the treatment. The invention also pertains to installations for the implementation of such a process.
Known in the state of the art are many thermal, thermomechanical, hydrothermal or hydrothermomechanical processes for the treatment of biological substances which are designed to modify their qualities.
However, in the various classic operations, the temperature level employed remains routinely limited by the fact that in order to reach the intended objective while still preserving the quality, the higher the temperature employed the more necessary it is to reduce or better control the duration of the treatment.
Nevertheless, the higher the temperature level, the shorter is the required treatment time. But the difficulties in controlling brief durations of treatment and the importance of the relative errors stemming from the durations of heating and cooling considerably reduce the application of relatively elevated temperature levels. Operations of the High-Temperature, Short-Time (HTST) type therefore remain generally a particularly difficult goal to reach outside of the cases of liquid products or products that have a liquid carrier.
The goal of the present invention is to resolve these shortcomings by proposing in the case of all of these operations and all of these envisaged products a very high degree of control of the treatment temperature/duration set of values capable of implementing the operation, accelerating its kinetics and preserving the desired quality of the finished product. The use of high temperature is coupled with a very high degree of control of the duration of treatment by means of a very rapid elevation of temperature and an equally rapid cooling by controlled instantaneous pressure drop down to a determined level of generally reduced pressure. Cooling is thus obtained by self-vaporization of the water and volatile compounds contained in the product because of the descent to vacuum. The final temperature level is primarily a function of the final pressure in the case of a given product.
In most of the envisaged operations and treatments, the mechanical effect is a function of the difference in pressure and temperature before and after the pressure drop and is above all caused by the amount of vapor generated by self-vaporization of the water and other volatile compounds initially present in the product. Its impact, which also depends on the specific thermohydrorheological behavior of the product, can often enable acceleration of numerous envisaged operations and thereby reduce the treatment time. Implementation of a high degree of control over its impact is also facilitated by the intermediary of the high degree of control over the initial pressure and temperature, the final pressure and especially the elapsed time of the pressure drop.
The present invention consists of providing for a very rapid heating of the product, by specific methods which depend on the product in question, on its form, on its structure and the desired objective, coupled with the imposition of a total pressure xe2x80x9cPoxe2x80x9d. These two operations of heating and application of pressure can be obtained in a coupled manner by injection of dry or wet steam. The operations can also be implemented separately by the use of other heating sources (microwaves, IR, conduction, convection, etc.) coupled with the injection of a suitable gas capable of providing the required high pressure. The invention is characterized in that one then proceeds to a subsequent step comprising a pressure drop down to a lower pressure. The abrupt drop in pressure down to vacuum can be controlled between two limits: the most instantaneous possible pressure drop so as to reduce the cooling time xe2x80x9ctrxe2x80x9d of the product and, possibly, a rather long pressure drop time in order to reduce the expansion phenomena to a level below 1.5. According to a preferred mode of implementation, the duration of the abrupt pressure drop is a function of the product to be treated, its form, its dimensions and the envisaged quality. It is routinely comprised between instantaneity and several seconds. If the operation of heating and application of pressure is implemented in a chamber, the drop down to the reduced pressure can be obtained by application of a vacuum in the chamber in question by connection to a vacuum tank of relatively large volume, or by mechanical passage of the product into a reduced pressure medium; the two possibilities can also be implemented simultaneously.
The process of treatment by controlled instantaneous pressure drop is known, for example, from the description in French patent FR 93 09 728. This treatment process produces a modification of the texture of the biological product by a rapid expansion of the material. It enables production of expanded products, particularly from fruits or vegetables, which are crisper and more agreeable to eat, or to facilitate their subsequent hydration. The effect produced by this process of the prior art is a significant expansion of the volume to a level larger than 1.5. This application is not relevant to the present invention which is limited to applications that create a very slight expansion of levels routinely lower than 1.5. Nevertheless, the installations which are the object of the present invention can also be used in the process defined by the cited patent.
Also proposed in the prior art was a process for the extraction of juices and fragrances from plant substrates as described in patents FR 26 38 333, FR 88 14 311, FR 89 17 414, FR 92 05 669, FR 93 13 186 and FR 93 13 287. This process is designed for the heating and rapid application of vacuum to a plant material so as to modify its structure and induce the gravitational flow of a juice rich in fragrances with the emission of other aromatic vapors which are recovered separately in the form of condensates. This process is not satisfactory in practice because the energy of the pressure drop is devoted principally to the destruction of the material which facilitates the subsequent extraction by steam distillation. The process which is the object of the present invention concerns precisely the replacement of the steam distillation operation by heating followed by a particularly abrupt pressure drop so as to lead to a self-vaporization operation of various volatile compounds at the final reduced pressure. The self-vaporization of the compounds present according to their thermodynamic properties forms a clear acceleration over steam distillation by the use of the adiabatic and isentropic transformation of the pressure drop down to reduced pressure. The process which is the object of the present invention is thus not linked to the structural breakdown of the material and can also treat mixtures of miscible or nonmiscible liquids as well as plant materials. Here, multiple cycles of heating and pressure drop down to vacuum are therefore often necessary in order to implement the self-vaporization of the mixture of the liquids according to their thermodynamic characteristics and their respective vapor pressures at the treatment temperature.
The applications of the process according to the invention pertain generally to debacterization, pasteurization and sterilization, modification of the structure of the treated materials, separation of their components, preparation of fruits or vegetables so as to facilitate their peeling and/or their pressing, enhance the quality of the finished product or extract, increasing the value of the by-products or reducing the technical steps of the operations, etc. The present invention pertains to the precise control of these treatments by means of controlling the temperature and the duration of thermal, hydrothermal, thermomechanical and hydrothermomechanical treatments.
For this purpose, the present invention in its most general form pertains to a process for the treatment of solid products, especially of biological products in piece, powder or paste form, and of miscible or nonmiscible liquid products, comprising a step of heating the products under pressure for a period of time xe2x80x9ctrxe2x80x9d, characterized in that the process comprises subsequent to the heating step, a step of cooling by pressure drop down to vacuum.
According to a first variant, the heating step is implemented under a pressure greater than or equal to 0.8 bar.
According to another variant, the heating step is implemented by injection of wet or superheated steam.
According to a third variant, the heating step is preceded by a step comprising reduction of the pressure in the treatment chamber, with the pressure before heating being less than 0.2 bar.
According to a fourth variant, the cooling step is implemented by a pressure drop down to a pressure lower than or equal to 0.5 bar.
These different variants are not mutually exclusive and can be combined among each other.